Temperature effect on the removal of hydroxyl radical by a polycrystalline platinum surface

The catalytic removal of OH radicals by a polycrystalline platinum surface has been studied in a low-pressure discharge-flow system. OH radicals, generated in a microwave discharge, were passed over the Pt surface and detected downstream by using the laser-induced fluorescence (LIF) technique. The activation energy for the removal of OH by Pt over the temperature range of 300-900 K was found to be 3.6 ± 1.3 kcal/mol. Above 950 K, OH started to desorb from Pt as was previoulsy demonstrated. A reinvestigation of the thermal desorption of OH over a broad range of temperature and the O/H ratio revealed that the activation energy for OH desorption depends strongly on the O/H ratio, varying from 27 kcal/mol at O/H = 100 to ∼51 at O/H = 0.037. Both the removal and desorption processes are believed to occur primarily on weaker surface sites because of the high coverages under the present flow conditions.